This invention relates to a tubular medical instrument such as a sound, catheter or endoscope having a flexible tube. Particularly, it relates to a tubular medical instrument having a cuff-equipped flexible sheath which is to be inserted into a human body cavity, for example stomach or small intestine, for a medical treatment.
Generally, the flexibble sheath of such tubular medical instrument advances deeper into the human body cavity, helped by the peristaltic movement of, for example, the small intestine. But it takes a long time to insert the flexible sheath in this manner. Thus, the sheath is often forced into the human body cavity by not only the peristaltic movement but also external force. If this is practiced, the patient suffers inevitably a greater pain.
To lessen such pain, the applicant has proposed in U.S. Pat. No. 4,066,070 issued Jan. 3, 1978 a tubular medical instrument having a flexible sheath which has a plurality of cuff assemblies on its forward portion. Each cuff assembly is constituted by a main cuff with a doubled-back section which can be deformed while held in rolling-contact with the wall of the body cavity and an auxiliary cuff disposed rearward of the main cuff and made expansible only in a radial direction of the sheath. Air is selectively introduced into these cuffs to expand them. The expanded cuffs broaden the body cavity. Then the operator inserts the sheath farther in the human body cavity. Since, there is no excessive friction between the sheath and the wall of the body cavity, the insertion of the sheath is smoothly carried out, without pressing the wall of the body cavity too hard.